If the tablet’s display is misbehaving even when no buttons are being pressed, then please try a hard boot by removing the battery and reinserting it. Also, try a factory reset of the device to replace the software with a new configuration.
Based on the errors you are getting, the filesystem on the tablet’s hard drive appears to be corrupt. If the tablet is brand new, then you are in luck because you should be able to refund/exchange it. Please return it soon (hopefully you still have the receipt).
If the LAN port lights up, then it is functioning and does not need to be replaced. The next step would be to go to the PC’s Device Manager utility at devmgmt.msc and uninstall/re-install the drivers for the Ethernet adapter.
If you can connect to Facebook, then your Internet isn’t completely down. Try recycling the connection by turning Airplane Mode on, and then re-starting the internet connection. Also, please see if there are any system updates pending for your device.
If the issue started when the customer dropped their iPad, then the damage may be hardware-related. Reinstalling iOS may not help in this case, and fixing it might require actually opening up the device, if possible. Is the customer’s data backed up to iCloud (you may have already considered this)? Because if it is, it’s already safe. Please make sure that iTunes has been updated to its latest version. Error codes that appear when you try to connect to iTunes can sometimes be caused by security software on the computer blocking access to the external device. See if temporarily disabling any anti-malware programs doesn’t help.
Have you tried booting from a DVD drive that you can attach to your Mac via USB? They sell these types of DVD drives at Walmart and Best Buy, among other stores. If that doesn’t work, then the problem may be with the Mac installation itself. Try reinstalling a new copy of the macOS and starting over. Turn on the Mac and press and hold command +r until you see the Apple logo. This will launch macOS recovery, and “Reinstall macOS” will be one of the options.
The only place where you can download Windows 10 safely is directly from Microsoft’s website because Windows is proprietary software. Please download your Windows 10 ISO from Microsoft. Windows 10 works best with a GPT-formatted hard drive, UEFI mode, and Secure Boot enabled. Please verify all these settings before proceeding with your installation. You may be correct about your hardware being legacy hardware. Windows 10 requires a CPU with PAE, NX, and SSE2 technologies that Windows 7 does not need. If installing Windows 10 proves impossible, you may have to reinstall Windows 7.
If your computer has gotten slower and hot to the touch, it may be infected with malware. Malware can monopolize a computer’s resources and make it overheat and become painfully slow. Before you try anything invasive - like replacing the hard drive - try running a good anti-malware program on your PC. Malwarebytes has a free version of anti-malware software on their website that you can download and run on your system. You may also try defragmenting the hard drive to make it run faster. Type defrag.exe in the Search Box on the Taskbar at the bottom of your screen to open the “Defragment and Optimize Drives” app. The app will offer options you can click on to optimize your hard drive.